Final Diagnosis -- Metaplastic Carcinoma of the Breast

Spindle cell carcinoma of the breast (SpCC) is a rare variant of metaplastic carcinoma in which the spindle cell component predominates; it presents as a wide spectrum of findings with mildly atypical features resembling a reactive process such as fasciitis, fibromatosis or granulation tissue reaction or with more malignant features resembling a low-grade sarcoma. The largest series of SpCC of the breast to date was reported in 1989 by Wargotz et al. (1) and defined as an intraductal or infiltrating carcinoma (ductal, lobular, squamous or mixed) that is contiguous or subtly merges with a blend, monotonous-appearing spindle cell proliferation that comprises more than half of the neoplasm.

SpCC is mainly diagnosed in postmenopausal women with the average age of 63, but it can be present between ages 29 and 95. The clinical presentation is that of a single, palpable, firm breast mass, located most often in the upper outer quadrant. The tumor is painless and, in the majority of the cases, presents without axillary enlargement.

On gross examination the tumors are firm to hard, well circumscribed or ill defined and could measure from less then 1 cm to over 20 cm. They are pink-tan and frequently mottled, with one or more cysts.

Microscopically, the main features include the presence of two distinctive components that are necessary for the diagnosis (1):

A dominant population of bland-appearing bipolar cells with plump nuclei, insignificant pleomorphism and low mitotic activity, growing in a feathered or more storiform pattern.

In situ or infiltrating ductal, lobular or mixed carcinoma that is contiguous or subtly merges with the spindle cell component.

Differential diagnosis:

Malignant tumors

Malignant fibrous histiocytoma (MFH)-Fibrosarcoma, which may present with storiform pattern areas, but is not associated with intraductal or infiltrating duct carcinoma or a squamous component and does not show angiod areas. The presence of tumor giant cells and the characteristic immunostaining pattern for MFH helps in distinguishing these two entities.

Carcinosarcoma, typically shows biphasic pattern with epithelial and mesenchymal component that don't merge with each other and easily can be distinguish form SpCC, even in those cases where the stroma shows some immunoreactivity for Keratin.

Benign tumors: when the presence of an overt carcinoma is ruled out by thorough sampling of the lesion, several very rare lesions of the breast should be considered

Fasciitis has a rapidly growing cellular proliferation of fibroblasts resembling granulation tissue and shows a myxoid background with scattered lymphocytes and erythrocytes. Mitotic figures are numerous, but abnormal mitoses are rarely seen. There is no epithelial component.

Fibromatosis is a hypocellular lesion of the breast with abundant collagen, lacking nuclear hyperchromasia and showing infrequent mitosis. Similar to fasciitis, fibromatosis shows no epithelial component.

Prognosis

The cumulative 5-year survival for SpCC is 64% (1) and is higher survival rate as compared to the metaplastic carcinoma overall.

SpCC tends to recur in approximately 56% of the case (1), both as local recurrences or metastasis. The recurrence rate depends on the initial treatment, as well as the gross and microscopic tumor characteristics, with tumor size and microscopic circumscription showing significant difference (1)(Table 2).
Table 2 (from Wargotz et al.)
The pathologic features of SpCC in recurrent an non-recurrent neoplasms